The invention relates in general to weapon systems and in particular to testing systems for weapon systems.
Upon impact with a target, a projectile's terminal ballistic performance is highly dependent on numerous factors. These include: impact velocity, bullet orientation, bullet construction, target composition, target orientation and test geometry. Target orientation, target composition, and test geometry are easily controlled for during tests. Additionally, there are established methods for determining impact velocity which have been employed with great accuracy. However, it is a challenge to measure the orientation of the bullet during tests.
Bullet orientation includes both angle of obliquity and angle of attack (AoA). Angle of obliquity is the angular difference between the normal vector of the target surface and the velocity vector of the incoming projectile. During testing, the angle of obliquity can be controlled by orienting the target surface to be normal to the bullet trajectory at impact location.
AoA, however, cannot be controlled for during testing and must be determined. A projectile's AoA is the angular difference between the projectile's velocity vector and its longitudinal axis, also known as pointing direction. During flight, the longitudinal axis of an axially-symmetric spin-stabilized projectile rotates around its velocity vector in a profile known as epicyclic motion. When evaluating a projectile's impact effects on a target, the AoA is of particular importance because low AoA values indicate improved penetration performance.
While methods for measuring the AoA of a small caliber projectile exist, these conventional methods are inadequate as they are either inaccurate, costly or time consuming. Yaw cards are one approach that has been used to measure AoA. Yaw cards made from plastic paper or cardboard-like materials are placed at various locations along a bullet trajectory. The shape of the hole made in the card after the bullet passes through is then compared to a baseline to estimate the orientation angle at that location. These estimates are crude in precision, especially for small caliber projectiles. The setup and post-processing of yaw cards is often exhaustive. Additionally, new cards are needed for each test. In some test situations it may not be possible to place yaw cards at the point of impact because damage from spalled components may affect the shape of the hole.
Another common approach involves the use of “pitch and yaw” high speed video cameras. In such a method, camera systems are placed at the target location to record images of bullets before impact. The setup of these system along with illuminating bulbs can be exhaustive. Following a test, the results are usually analyzed manually by an operator clicking on various points of the projectile. This type of analysis can typically take days, if not weeks, of data reduction and it is difficult to verify the accuracy of the results. Additionally, because of spalling at impact, these expensive camera systems must be shielded using thick bullet-proof glass which can hinder results and further complicate setup.
More sophisticated methods of orientation measurement include shadowgraphs and radiographs. These images are generated by short duration pulses of light or x-rays which are similar to photographs. These images are collected between tests, digitized and the processed relative to template or background fiducial to develop orientation and position histories at each station. While these methods have been found to be accurate, the time required for analysis can be significant because of manual data and digitization.
Therefore a need exists for a system and method for determining the impact angle of a small caliber projectile that is both efficient and effective.